This invention relates to a process for increasing the melting point of mixtures of partially brominated diphenyl oxides having an average of 7.2 to 7.7 bromine atoms per molecule of diphenyl oxide.
The above mixtures are sold and denominated by the flame retardant industry as octabromodiphenyl oxide or as "Octabrom". For the sake of simplicity, these mixtures will hereinafter be referred to as Octabrom. Typically, the commercially significant Octabroms contain 0-2 weight percent pentabromodiphenyl oxide 5-15 weight percent hexabromodiphenyl oxide, 40-55 weight percent heptabromodiphenyl oxide, 30-40 weight percent octabromodiphenyl oxide, 5-15 weight percent nonabromodipnenyl oxide, and 0-2 weight percent decabromodiphenyl oxide. As can be appreciated, for any particular Octabrom, the average number of bromine atoms per molecule of brominated diphenyl oxide, hereinafter referred to as the bromine content, is dependent upon the amounts and the identities of the particular bromo homologs which are present in the mixture. The bromine content can be calculated by multiplying the weight percent of each bromo homolog by the number of bromine atoms in that homolog, adding the resulting products and dividing the sum by 100.
Octabrom has a melting point which is expressed as a temperature range since it does not exhibit a sharp melting point. Depending upon the process and any post-process treatment used for producing the Octabrom, the melting point can be low, e.g., mp 75.degree. C.-95.degree. C., high, e.g., mp 90.degree. C.-145.degree. C. or can be somewhere in-between.
It has been observed that the melting point of any particular Octabrom is an indicator of its amorphic or crystalline nature. The lower melting Octabroms are much less crystalline, i.e., more amorphic, than the higher melting Octabroms. Another difference between Octabroms with the lower melting points and Octabroms with the higher melting points is that the former has a tendency to form lumps and not to be free-flowing after being subjected to long storage periods, say a few weeks, and to elevated temperatures, e.g., 50.degree. C. to 80.degree. C., during the storage period.
Besides being an indication of the amorphic or crystalline nature of Octabrom and the tendency of the Octabrom to lump, the Octabrom melting point can also be a specification set by the Octabrom purchaser. Depending upon the use of the Octabrom, low melt or high melt Octabrom can be required.